1. Field of the Invention
The present invention relates to storage stable road paving asphaltic compositions having improved viscoelastic properties, softening points and, particularly, phase compatibility that are suitable for use as a binder in dense graded and open graded asphalt pavement and the process of making such asphaltic compositions.
2. DISCUSSION OF RELATED ART
Asphalt has certain physical properties that vary widely with changes in temperature. For this reason, polymers often are added to asphalt to extend the range of its physical properties. Polymers can reduce the tendency of the asphalt to creep and rut in warm weather by enhancing its high temperature viscoelastic properties; and polymers can minimize cracking and stripping in cold weather by improving the asphalt's low temperature viscoelastic properties.
Not all asphalts and polymers form compatible mixtures. Polymer modified asphalt's storage stability is greatly affected by the compatibility of the asphalt with the particular polymer. Incompatible and partially compatible mixtures undergo phase separation.
Various methods have been suggested for making polymer-modified asphaltic compositions that are sufficiently compatible to be acceptably storage stable and that also have the viscosities and softening points in the ranges required for a particular application. Some, for example, rely on selecting appropriate polymer and/or other additives to affect the final properties of the asphalt-polymer mixture (see, for example, U.S. Pat. No. 4,600,635 for use of a bitumen-based adhesive composition comprising bitumen, oil and an ionomeric elastomer, such as sulfonated, carboxylated or phosphonated EPDM or butyl rubber, in amounts less than 15% by weight of the mixture that is neutralized by metal cations; British Patent No. 1,534,183 for addition of from 5% to 95 % wt. of an ethylene/vinyl ester copolymer and bitumen partially crosslinked by means of --O--M--O--, O--B--O-- or --O--CRR'--O-- bridges; or U.S. Pat. No. 4,882,373 for acid modification of asphalt with subsequent contact with an oxygen-containing gas, and mixing with a thermoplastic elastomer, and unsaturated functional monomer.)
Others oxidize the asphalt before using it. U.S. Pat. No. 4,371,641 teaches that a polymer, preferably an unsaturated elastomer, e.g., EPDM or butyl rubber, or a thermoplastic polymer and an appropriate filler can be added to airblown asphalt to make it suitable for use as a roofing material by increasing the asphalt's stability towards oxidation and decreasing its sensitivity to ultraviolet radiation. Applicants' invention is an asphaltic composition that does not use airblown (oxidized) asphalt.
Accordingly, none of the foregoing references teaches nor suggests the process of making road paving asphaltic compositions, nor compositions themselves that have improved physical properties, particularly the unexpected result that in the composition the polymer and asphalt, although separate phases, do not segregate on standing at elevated temperatures.